1. Field of the Invention
This invention relates to a ferromagnetic resin composition obtained by subjecting rare earth-cobalt powder, which is a ferromagnetic powder, to oxidation-inhibiting treatment, and then filling a thermosetting resin with said powder in an amount of 70 to 97% by weight.
2. Description of the Prior Art
With the development of electronic and electric industries, the performance characteristics of magnets have been improved, and the use thereof has greatly been broadened and the amounts thereof have greatly been increased. Magnets which are most general and much used are sintered ferrite magnets produced by a powder metallurgy method. Their characteristics, when expressed in terms of maximum energy product (BH).sub.max, are approximately 1 MGOe in the case of isotropic magnets and 2 to 4 MGOe in the case of anisotropic magnets, and sintered ferrite magnets are markedly characterized in that they are very inexpresive as compared with other magnets. In addition, Alnico magnets are often used, and show such excellent characteristics as compared with ferrite magnets that their maximum energy products are 5 to 8 MGOe. However, they are disadvantageous in that they are expensive owing to the sudden rise in prices of raw material cobalt, tend to lose magnetic force because of a small coercive force Hc, and hence, the use thereof is limited. Further, recently, rare earth-cobalt magnets have come to be noticed in various fields because they have excellent magnetic characteristics. Although rare earth-cobalt magnets themselves are considerably expensive because rare earth elements per se and cobalt are both expensive, they are fairly often used in smallsized parts in which they can effectively exhibit their excellent characteristics.
The magnets described above are disadvantageous in that they are low in impact resistance and tend to crack because they are produced by casting or sintering. In recent years, there have been developed and widely used plastic magnets obtained by filling plastics with ferrite powder in order to improve the impact resistance. These magnets have a lower magnetic force than sintered magnets because they contatin a large amount of a plastic material which is a substance irrelevant to magnetism. In order to supply this deficiency, it has been tried to improve a technique for conversion to anisotropic by which the easy axes of magnetization of ferrite powder are aligned in one direction, and it has become possible to enhance the (BH).sub.max values of plastic magnets to 1.7 MGOe which is higher than those of isotropic sintered ferrite magnets. However, most of magnets having a (BH).sub.max of 2.0 MGOe or higher are anisotropic sintered ferrite magnets, Alnico magnets or rare earth magnets, which are brittle and hence said to be not usable in a considerable number of fields. In recent years, there have been invented plastic magnets obtained by impregnating rare earth-cobalt powder with epoxy resin powder, as magnets which can have a (BH).sub.max in the range described above and possess improved impact resistance. However, they are not yet sufficient in impact resistance and are disadvantageous also in that they cannot be recycled at all and hence become expensive after all.